1. Field of the Invention
This invention relates to an improved engine lubricating oil composition and a method for improving the operation of spark ignition internal combustion engines and diesel engines. More specifically, the invention concerns adding certain quaternary ammonium hydroxides to a lubricating oil to reduce combustion chamber deposits and the octane requirement increase in spark ignition internal combustion engines, and to improve oil consumption in diesel engines.
2. Description of Related Art
The octane requirement for a new or cleaned spark fired internal combustion engine is lower than that required for an engine that has been operated for several thousand miles. This is due to deposits accumulating in the combustion chamber of the engine such that an octane requirement increase (ORI) results; i.e., the octane number of the fuel required for knock-free operation of the engine increases with time until a stable level is reached. Consequently, various compounds have been added to the fuel to prevent or reduce the formation of deposits in the combustion chamber or to remove deposits already formed in the combustion chamber (See for example U.S. Pat. No. 4,357,148 and the patents cited therein, the disclosure of which are incorporated herein by reference). However, some additives may not survive combustion of the fuel to reach the deposits that cause ORI and, thus, will not be effective in reducing ORI.
In addition to the additives described in U.S. Pat. No. 4,357,148 and the patents cited therein, certain quaternary ammonium hydroxides have been added to gasoline to reduce carburetor deposits. For example, in U.S. Pat. No. 3,468,640, a particular class of quaternary ammonium hydroxides are added to gasoline to reduce deposits in the intake system caused by introduction of blowby and puffback gases. The class of hydroxides used is characterized in that one of four alkyl groups attached to the nitrogen atom is a methyl group and the length of the carbon chain in at least one of the other alkyl groups is from 10 to 24 carbon atoms. A specific quaternary ammonium hydroxide (choline) has also been added to fuels and lubricants to neutralize naphthenic acids as well as reduce the color and corrosiveness problems caused by said acids (see U.S. Pat. No. 4,600,518). However, due to the relatively few carbon atoms in choline, it is doubtful that choline would appreciably dissolve in the lubricating oil basestock or would survive the high temperature environment of the lubricant in an automotive engine. More recently, quaternary ammonium hydroxides have been added to gasoline to reduce ORI (See U.S. Pat. No. 4,787,916).
Diesel engine manufacturers have also been concerned about reducing the buildup of crownland and piston ring deposits in these engines because of the interrelationship between these deposits and increased oil consumption. Therefore, controlling deposit formation is important in reducing oil consumption in today's high performance diesel engines. Also, control of combustion chamber deposits is important in spark ignition internal combustion engines to obtain improved engine operation.
However, none of the above-mentioned references teach or suggest adding the specific quaternary ammonium hydroxides described herein to a lubricating oil to reduce ORI and combustion chamber deposits in spark ignition internal combustion engines and to reduce oil consumption in diesel engines.